A polymer gel is a soft material which is swollen by containing a large amount of water or an organic solvent as a medium in a three-dimensional network of an organic polymer, and widely used in various fields, such as medical, food, construction, and sport fields. In particular, a polymer gel containing water as a medium is called “polymer hydrogel”. In recent years, a nanocomposite hydrogel (below, abbreviated as “NC gel”), which contains an aqueous medium in a three-dimensional network obtained by using a delaminated clay mineral as a super-multifunctional crosslinking agent for an organic polymer, has been attracting attention as a polymer hydrogel having high water-swellable properties and excellent mechanical characteristics (Patent Document No. 1). However, in general, the polymer hydrogel containing water as a medium has a problem of drying in the atmosphere.
The NC gel also has the same problem. When the NC gel is allowed to stand at room temperature and is exposed to the atmosphere, the moisture in the NC gel gradually evaporates and the NC gel is dried. Some methods for inhibiting drying resulting from leaving in the atmosphere have been suggested. For example, Patent Document No. 2 discloses a polymer gel maintaining flexibility without drying, which is obtained by using a low volatile medium, such as glycerin, and 1,3-butylene glycol, instead of water. In addition, Patent Document No. 3 discloses a technique of covering the surface of the polymer hydrogel with a water-impermeable material. Although, a small amount of water can be contained together with the low volatile medium in the polymer gel disclosed in Patent Document No. 2, the main medium is the low volatile medium, not water. The polymer gel disclosed in Patent Document No. 3 is not a polymer gel containing water as the main medium. In addition, since the polymer hydrogel is entirely covered with a different material in Patent Document No. 3, the surface of the polymer hydrogel does not have hydrophilicity as a hydrogel, and water does not move in and out through the surface of the polymer hydrogel. The polymer hydrogel in Patent Document No. 3 does not have the inherent properties of the polymer hydrogel. It is thought that a polymer hydrogel containing a large amount of an aqueous medium and having nondrying properties which is not dried under general atmospheric conditions, and a polymer hydrogel having both nondrying properties and excellent mechanical properties (for example, excellent elongation properties, compression properties, and surface adhesiveness) can be effectively used in various fields in the atmosphere. Due to this, development of the polymer hydrogel has been expected.